536 EEPORT— 1889. 



these difficulties, and tased upon this decomposition a method of manufacturing' 

 aluminium on an industrial scale. The mode of procedure is briefly as follows: — 



Crj'olite mixed with an equal weight of salt is fused in a reverberatory furnace, 

 the molten charge is run into an iron ' converter/ and into the molten mass the 

 sodium necessary for the decomposition of the cryolite is introduced in small 

 quantities, some 5 lbs. at a time. By a special apparatus the sodium is immediately 

 immersed in the molten bath of cryolite and salt, and in this way loss by volatili- 

 sation and by burning of the sodium completely guarded against. After ' dipping/ 

 (as this operation is styled,) the charge with the required quantity of sodium, the 

 greater portion of the slags is poured off, and the remainder containing the 

 aluminium is poured into an iron vessel, in which, after cooling, the mass of alumi- 

 nium is found collected together in a coherent mass, easily separated from the slag. 

 A pure cryolite worked in this manner gives at once practically pure aluminium. 

 To get rid of the influence of impurities in ordinary cryolite, a method of fractional 

 precipitation is used, the charge of molten cryolite in this case being treated first 

 with a portion only of the sodium required ; the slags are then poured off inta 

 another vessel and the remainder of the sodium added. The metal produced from 

 this second dipping is practically pure aluminium, whereas that from the first 

 contains the silicon and iron formed from the impurities in the cryolite. For the 

 manufacture of the best brands of aluminium the above operations are conducted 

 in crucibles. 



The production of one part by weight of aluminium requires the following 

 amounts of materials : — 12 parts of cryolite, 12 of common salt, 20 of coal, and 3 of" 

 sodium, and 20 parts by weight of slags are produced, containing about 40 per cent., 

 sodium fluoride, 15 per cent, undecomposed cryolite, 43 per cent, salt, a small 

 amount of alumina, and a little aluminium. The slags by treatment with copper 

 may be utilised for the production of an aluminium bronze, and subsequently the- 

 sodium fluoride contained in the slag after removal of the aluminium in this way 

 may be converted into cryrdite by treatment with aluminium sulphate, when, 

 cryolite is produced as represented by the following equation : 



12NaF + Al3(SO,)3 = 2(Na3AlF6) + 3Na,S0,. 



A portion of the paper dealt with a description of the manufacture of sodium 

 from caustic soda by Professor Netto's process, which consists essentially in 

 allowing a stream of liquid caustic soda to flow over a mass of charcoal, heated in 

 a vertical cast-iron retort. The vapours of sodium and gaseous products are con- 

 ducted through a condenser and the liquid sodium collected in iron dishes. In this- 

 process only a portion of the sodium of the caustic soda is obtained as the metal, 

 some being converted into sodium carbonate, and this, together with the unaltered 

 caustic soda, collects at the bottom of the retort, forming a slag which is used 

 largely by paper-makers in place of pure caustic soda. By operating in this man- 

 ner the fact that caustic soda is decomposed by carbon at a comparatively low- 

 temperature is fully utilised, and consequently the decomposition can be effected in. 

 cast-iron retorts, whereas to completely decompose caustic soda by carbon a much 

 higher temperature is required, and vessels of cast-steel or wrought-iron employed^ 

 inasmuch as a portion of the caustic soda is converted into sodium carbonate, 

 which dikites the caustic soda and itself requires a very high temperature for its 

 decomposition. 



By this method 1 part of sodium requires the following proportions of material* 

 for its production:— 10 parts of caustic soda, 1-2 parts of cast-iron for retorts, 12 

 parts of coke for heating retorts, and 1-5 parts of charcoal for the reduction of the 

 caustic soda ; at the same time 9 parts by weight of slag, consisting of carbonate of 

 soda and caustic soda, are produced. 



The author expressed his indebtedness to Professor Netto and to the Alliance 

 Aluminium Company for the manner in which they had so kindly aided him in the 

 preparation of the paper, and for the specimens, diagrams, and photographs used in 

 its illustration. 



